What causes the Yamaha Xunying 125 to lack acceleration?

[McEvan]

Reasons for the Yamaha Xunying 125 lacking acceleration: fuel system malfunction, decreased engine compression ratio. Detailed explanations of the causes are as follows: Fuel system malfunction: Excessive fuel leads to an overly rich air-fuel mixture, causing the motorcycle to lack acceleration at low speeds. An overly rich mixture lacks sufficient oxygen during combustion, resulting in incomplete combustion. This reduces power output, worsens fuel efficiency, and easily leads to excessive carbon buildup, which can block the exhaust system and exacerbate the lack of acceleration. Decreased engine compression ratio: Engine power is directly linked to the compression ratio. With prolonged use, internal engine components wear out. If key components become excessively worn, the engine's compression ratio will decrease.